light from the eye of the observer, and an arithmetic device that detects Purkinje images and an iris image...http://www.google.de/patents/US6104431?utm_source=gb-gplus-sharePatent US6104431 - Visual axis detecting apparatus and method including scanning light source, and image device using same Erweiterte Patentsuche Ver???ffentlichungsnummerUS6104431 APublikationstypErteilung AnmeldenummerUS 08